LISA: The Science and the InstrumentRobin StebbinsU.S. LISA Project ScientistGoddard Space Flight CenterPhysics 798GUniversity of Maryland, College Park1 May 20072LISA Overview The Laser Interferometer SpaceAntenna (LISA) is a joint ESA-NASA project to design, buildand operate a space-basedgravitational wave detector. The 5 million kilometer longdetector will consist of threespacecraft orbiting the Sun in atriangular formation. Space-time strains induced bygravitational waves aredetected by measuringchanges in the separation offiducial masses with laserinterferometry.LISA is expected to detect signals from merging massive black holes,compact stellar objects spiraling into supermassive black holes in galacticnuclei, thousands of close binaries of compact objects in the Milky Wayand possibly backgrounds of cosmological origin.3LIGO and LISA4Gravitational Waves: A new way to study the Universe Signals direct from the most extreme conditions throughout theUniverse– Radiation from the primary objects, not secondary processes– Source dynamics are directly encoded in the waveforms. High precision measurements with simple interpretations– High signal-to-noise enables precision measurements of mass, spin, anddistance– Systems are simple, have few parameters, and are well described by GeneralRelativity Most powerful events in the Universe– Any pair of merging black holes - of any size - produce more energy than all thestars in the Universe. Many phenomena not observable in any other way– Phenomena are too obscured or too far away or simply electromagneticallydark– Gravity shapes the Universe. What better to map the Universe with!5The LISA SkyMassive and intermediate-mass black hole binaries• 102 - 107 M• z < 20• 10’s to 100 per yearUltra-compact binaries• ~1 M• Galactic and extragalactic• 1000’s - 10,000• Confusion foregroundExtreme mass-ratioinspirals• ~10/ 106 M• z < 1• 10’s - 100 per yearCosmological back-grounds, bursts and unforeseen sources6Sources and Science ObjectivesNew physics: cosmicbackgrounds andsuperstring burstsFormation and growth ofmassive black holesPrecision tests of GeneralRelativityDynamics of stars ingalactic nucleiDynamical strong-fieldgravityEvolution of ultra-compactbinaries in the Galaxy7What do we measure? Observe waveforms frommonths to years–10’s to 100’s of thousandsof cycles–SNRs from 10 to more than1,000s Waveform depends on 17parameters–Intrinsic parameters of thesource–Extrinsic parameters of theobserver Detection vs parameterestimation … an importantdistinction8Detection with LISA9Understanding the Formation and Growth of MBHs Massive black holes grew from one of two kinds of seeds– Large stellar mass black holes (~100 M) left over from the first stars (Pop III)at z>20– ~104-5 M black holes formed directly by the collapse of supermassive starclusters or gas clouds z~15 Massive black holes must grow at least fast enough to form ~109 Mquasars at z~6.4 (~1 Gyr after the Big Bang).– Accretion– Mergers– The gravitational rocket LISA will detect ~104 M black holes merging at z=30 with SNR=10. LISA will observe 300 M black holes merging with ~104 M blackholes at z=10 with a luminosity distance uncertainty of >35%,redshifted masses <1%, spins <0.2.10Merger Rates11Trace the merger history of MBHs and their host galaxies  The standard model of hierarchical structure growth calls for– Formation of small dark matter haloes– Formation of proto-galaxies within those haloes– Progressive mergers to form modern galaxies Coevolution of galaxies and massive black holes– Scaling relations between MBH masses and galaxy properties (e.g.bulge mass/luminosity, velocity dispersion) over >3 decades suggestthat MBHs grow in conjunction with their host galaxies. LISA will observe a wide range of merger events betweenz=10 and the present:– At z=10, events with total masses ranging from ~104 to 106 M, withluminosity distance uncertainties <35%, mass uncertainties <1%, spinuncertainties <0.2– At z=1, events with total masses ranging from ~105 to 107 M, withluminosity distance uncertainties <0.4%, mass uncertainties <1%, spinuncertainties <0.01– Mass ratios can range from 1000 to 1.12Merger Trees LISA will produce a sourcecatalog with the 17parameters, and theiruncertainties. Accretion will spin up MBHsto near maximal values Mergers will randomize spinsand leave relatively lowaverage spins. The gravitational rocketshould preferentially affectlower mass haloes and nearequal mass mergers. MBHs (~104 M) formed inglobular clusters may alsomerge with central MBHs,revealing other galacticdynamics13Survey binaries of stellar mass objects There are an estimated 26 million compact-star binaries in theMilky Way that will radiate appreciable gravitational radiationin the LISA band.– Mostly WD-WD binaries– Some NS-NS binaries– Possibly a few BH-BH binaries LISA should separate about 10,000 of them. There are currently about 10 known sources that LISA candetect, making them guaranteed gravitational wave sourceswith optical counterpart. Many more will be known by thetime that LISA flies. The known sources can be used to verify the14Science with stellar-mass binaries Study demographics of theseendpoints of stellar evolution Study exotic binary systems,e.g., common envelope, contactbinaries Map the distribution of thesestars in the Milky Way15Testing theories of relativity Stellar mass black holes (~10 M) will be gravitationallyscattered into highly eccentric orbits about central MBHs(~106 M). These “Extreme Mass Ratio Inspirals” (EMRIs) areestimated to occur at the rate of 20-40 per year out to z~1. SMBH mergers (~106 M) result from the mergers of their hostgalaxies, and are estimated to occur at the rate of a few peryear. Observations of compact-star binaries will directly verify thepropoeries of gravitational waves four decades of frequencybelow the LIGO band. The “verification binaries” alone willdirectly confirm16Waveforms “Verification binaries” will directlyconfirm the properties ofgravitational waves four decadesbelow the LIGO band with knownsources. EMRIs have rich waveforms whichenable :– Mapping the spacetime around– Testing the “No-hair Theorem” ofGeneral Relativity to ~1% accuracy– Measuring the dynamical tide onhorizon to ~10%